U.S. Pat. No. 3,519,503 to Moore et al entitled "Fabrication Method for the High Temperature Alloys", of common assignee herewith, describes a forging process developed by Pratt & Whitney Aircraft, Division of United Technologies Corporation, Hartford, Connecticut and known internationally as the GATORIZING.RTM. forging process. By the disclosed process, high strength, difficult to forge alloys such as those used in the gas turbine engine industry, are deformable from a billet of stock material to a nearly finished shape of relatively complex geometry. Although, only disk-shaped components were initially forged, the attractiveness of forming integrally bladed rotor disks spurred subsequent developments.
An initial die package and process for forming such integrally bladed rotors is disclosed and illustrated in U.S. Pat. No. 4,051,708 to Beane et al entitled "Forging Method" and in the divisional case thereof U.S. Pat. No. 4,074,559 to Beane et al also entitled "Forging Method". Both patents are of common assignee herewith. In accordance with these concepts, integral appendages are forged between a plurality of adjacent dies positioned about the circumference of the disk forming dies. Yet further advances include the techniques for separating the appendage forming dies from the finished forging. Two such techniques are illustrated in U.S. Pat. No. 4,040,161 to Kelch entitled "Apparatus and Method for Removing a Plurality of Blade Dies" and 4,150,557 to Walker et al entitled "Forging Apparatus Having Means for Radially Moving Blade Die Segments".
Commonly owned U.S. Pat. No. 4,312,211 and 4,265,105 both by MacNitt, Jr. et al describe a forging method and apparatus wherein two concentric dies are moved sequentially against a billet to form the forged component in two steps. The first die is moved and compresses a billet to an intermediate configuration. The first die is then held stationary against the partially compressed billet while the second die is moved to compress the billet to a final configuration.
In several of the foregoing patents (e.g. 4,252,011) the forging apparatus described is an automated one, wherein a die package is first assembled and then automatically moved into position within a bull ring and is heated to forging temperatures, whereupon the actual forging step takes place. The die package, containing the finished forging, is then automatically moved to another station and the forged part is removed.
It is required, for some forged parts, that tolerances on the as-forged part be extremely close. This requires that the appendage forming die segments be precisely located at the time of and during forging. Two separate problems have been discovered in connection with this requirement. The first problem is initially assembling the die package with the die segments precisely located relative to each other, and being able to move that die package into position between the forging dies without any of its components moving out of position. The second problem involves maintaining the die segments in position throughout the actual forging step. If the die segments are not correctly located at the time of assembly, or if they move somewhat as the die package is moved into the forging press, then it will make no difference that the die package is held stationary throughout the forging process, since the die segments will not be in the proper position to begin with. On the other hand, if the die package is precisely and accurately positioned at the beginning of the forging cycle, the finished component may not meet required tolerances if, during the forging cycle, the die segments move out of position. The problem is aggrevated when parts of complex shape, such as disks having highly twisted airfoils integral therewith, are being forged.
Commonly owned U.S. Pat. No. 4,252,011, MacNitt Jr. et al describes apparatus for preventing relative tilting (i.e. for stabilizing) the die segments of a die package throughout the forging operation. More specifically, annular ring forming means are disposed in interlocking relationship with the inner circumferential surfaces of the appendage forming die segments. The MacNitt Jr. et al invention has not proved to be totally satisfactory in all cases, particularly when forging centrifugal rotors having blades with unusually high degrees of twist.